1. Field of the Invention
This invention relates to a process for the preparation of polyamides and related compounds and is more particularly concerned with a continuous solvent-free process for the reaction of organic diisocyanates with dicarboxylic acids and related compounds to form the corresponding polymers containing recurring amide linkages.
2. Description of the Prior Art
The preparation of polyamides, i.e. polymers which contain a recurring amide linkage, by reaction of organic diamines with dicarboxylic acids and derivatives thereof such as acid chlorides, is well-known in the art. Such processes include solvent-free reactions in which the polymer is produced by melt condensation of the reaction components. Where the reactants are diamines and dicarboxylic acids, the reaction produces water of condensation and a number of methods of separating the water as steam from the reaction mixture are known. Illustrative of such methods and apparatus for achieving the result are those described in U.S. Pat. Nos. 3,477,094; 3,492,791; 3,493,031; and 3,773,738.
More recently the production of polyamides by reaction of organic diisocyanates with dicarboxylic acids and related compounds has been described; see, for example, U.S. Pat. Nos. 4,087,481; 4,115,372; and 4,156,065. In the case of these latter reactions the condensation results in the elimination of carbon dioxide. Hitherto, the reaction has been conducted in the presence of inert organic solvents. However, for commercial production the use of organic solvents of the type required is extremely undesirable both from the point of view of economics and from the requirement to avoid pollution of the atmosphere by discharge of such solvents from production facilities.
So far as Applicants know no method has previously been described which enables the reaction between the diisocyanate and the dicarboxylic acid to be carried out in the absence of such organic solvents. In particular, no such solvent-free reaction which can be operated on a continuous basis has been described.
It is an object of the present invention to provide a process which can be carried out continuously and in the absence of inert organic solvents and which can be used to produce polymers containing amide linkages by reaction of organic diisocyanates with dicarboxylic acids or related compounds.